a b s t r a c tTarnishing is produced by reaction of silver with gaseous reduced sulphur compounds from atmospheric pollution. It induces the formation of Ag 2 S crystals which produce a dark appearance. To remove sulphur tarnishing, different mechanical, chemical and electrochemical methods have been traditionally used. To assess the effect of different cleaning treatments on tarnished silver, coupons of pure and sterling silver (92% Ag/8% Cu) were subjected to six cycles of induced tarnishing and cleaning. The cleaning methods evaluated were mechanical (soft abrasives and rubber point mounted on a rotary tool); chemical (chelating and acid solutions) and electrochemical (potentiostatic reductions). Surface morphology, composition, weight, color and luminosity were evaluated by optical microscopy, scanning electron microscopy/energy dispersive X-ray spectroscopy, atomic force microscopy, X-ray photoelectron spectroscopy and colorimetry. The cleaning impact on tarnished silver depended on the cleaning procedure and the composition of silver. Mechanical treatments restored the original visual appearance of silver although they produced a significant mass loss and a fast re-tarnishing. Chemical cleaning methods were fast; nevertheless the surface appeared completely attacked. Electrochemical cleaning did not yield good result for sterling silver, but was an effective cleaning method for pure silver coupons. Different cleaning methods have been used for many years to remove sulphur tarnishing from silver. However, scientific studies which assess the treatment's impact on silver and the re-tarnishing rate are very scarce. Costa [1] carried out a complete bibliographic study about the cleaning procedures and their applications, although the results of these different scientific works are difficult to compare since they have not been systematically evaluated in similar conditions and materials.The aim of this study is to quantitatively assess the efficiency, residues left on the metal and impact on the base metal of eleven mechanical, chemical and electrochemical cleaning methods to remove tarnishing on pure and sterling silver. To evaluate the effect in the long term, several cycles of tarnishing/cleaning are considered.

No abstract

No abstract

No abstract

During the sixteenth century the process of the conquest of Mesoamerica was complex and it took more than 50 years to suppress the resistance of the Indian population. In that length of time Augustinians played a prominent role. St. Nicholas of Tolentino monastery was designed to exercise charity and today it is one of the most important heritage buildings in the State of Hidalgo, Mexico. The Augustinian Hermits had a devotion to reading and studying of sacred scriptures and used the monastery and the church during several years. In spite of frequent conflicts during the nineteenth century in Mexico the church and the convent still preserve their original architecture. By the second half of the twentieth century the monastery declined, and the Mexican government decided to restore it. The purpose of this paper is to expose benefits of using recent surveying methods, as well as the possible reuse of the monastery as a gallery. Also with the help of a MALA ramac X3M radar we surveyed specific wallsand certain floor surfaces inside the church, in order to find undiscovered rooms. Non destructive evaluation techniques can be useful to determine the reuse of historic buildings.